In handle grips of motorcycles and snowmobiles used in cold districts, electric heating wires are installed within handle grips made of synthetic rubber for warming hands of users as described in, for instance the following Patent Document. In this known handle grip, an electric heating wire is wound helically around a core body made of a synthetic resin such that the electric heating wire is installed within a groove formed on the surface of the core body. Then, an assembly of the core body and heating wire is covered with a synthetic rubber by molding.
The Patent document 1: U.S. Pat. No. 4,990,753